The quantity and variety of pollutants introduced into our lakes, rivers and streams from domestic and industrial sources has increased at an alarming rate in recent years. Pollutants ranging from organic wastes to toxic chemicals have been found in surface waters at levels far in excess of the water's natural capability to oxidize them. In an effort to improve water quality, domestic and industrial polluters have been required to develop treatment systems capable of removing a substantial amount of the organic and inorganic wastes from the water they utilize, prior to its return to surface water sources.
Several prior art systems have been developed for the treatment of water contaminated with organic wastes, cyanides, phenolic compunds, heavy metals and the like. The term "water" as used herein is intended to include any water containing undesirable contaminants or impurities, including but not limited to, the above named impurities. A typical treatment system employed chlorine gas as the reactive agent. However, chlorine was found to have limited oxidizing and bond cleavage capabilities and proved to be difficult to use effectively in purifying the water. Systems using chlorine gas generally consist of several holding tanks, the pH of the water in each tank being carefully monitored and controlled within specific ranges throughout the treatment process. As the water to be treated is introduced into the first holding tank, the pH of the water is raised to about 12 and transferred to the second tank where a suitable flocculent is introduced, causing the metal ions produced by reaction with the chlorine gas to settle out of the solution for later removal by a filter. In a third tank, the pH is lowered to a range of 6 to 9.
The apparatus for this cumbersome treatment process is expensive to construct, and the operational costs are substantial as constant monitoring of the pH levels is required during operation. In addition, the bond cleavage capability of chlorine gas is limited. For example, chlorine gas will not react to break down the carbon-nitrogen bond found in cyanide molecules, such as sodium or copper cyanide, and these chemicals are very difficult to remove from water by filtration.
The superior bacteriocidal, viricidal, oxidizing and bond cleavage capabilities of ozone have been known for many years. However, the major factor preventing the widespread use of ozone in water treatment systems in this country, as an alternative to chlorine gas, is the prohibitive costs of purchasing, operating and maintaining existing types of ozone generators. Prior art ozone generators produce ozone primarily by electrostatic corona. Two or more discharging surfaces, which form a condenser with an air gap, are disposed at a distance from one another and may or may not be furnished with a dielectric element. A certain electrostatic flux density will cause pale violet light to appear adjacent the conductive surfaces. If the air between the conductive surfaces is adequately dehumidified, and proper levels of voltage and frequency are obtained, the discharge of electricity between the surfaces will be substantially silent, with very little discharge of sparks, and a high proportion of the generated light will consist of ultraviolet rays. This silent discharge or electrostatic corona produces ozone in a relatively highly charged state.
The efficiency of ozone production by electrostatic corona is dependent upon the shape of the surfaces of the electrode, the dielectric pressure, and the humidity of the air between the conductive surfaces. For optimum production of ozone a device for dehumidification is required, which adds substantially to the operating costs of conventional generators. Existing ozone generators are also expensive to purchase, requiring a sizeable initial capital investment. In addition, conventional generators produce oxides of nitrogen, which combine with water vapor in the ambient air to form corrosive nitric acid. Maintenance costs are thus relatively high as parts of the generators corroded by nitric acid may require repair or replacement.